KINASE SPECIFICITY Selective Targeting of a PKC Isozyme

Maeno-Hikichi et al. investigated protein kinase C (PKC) regulation of Ca²⁺ channels and discovered an adaptor protein that targeted PKC to N-type Ca²⁺ channels to form a functional signaling complex. At least 10 isozymes of PKC, a family of cytosolic kinases that translocate to the membrane after activation by diacylglycerol, are found in neurons. Although individual PKC isozymes are believed to mediate unique functions, the mechanisms underlying their specificity of action remain unclear. Maeno-Hikichi et al. used yeast two-hybrid screening of rat brain cDNA libraries to identify proteins that interacted with N-type but not P/Q-type Ca²⁺ channels and cloned enigma homolog (ENH), a protein known to bind PKC in vitro. Immunostaining revealed ENH expression in various brain regions and demonstrated that ENH was located in both neuronal cell bodies and presynaptic nerve terminals. The authors combined immunoprecipitation with Western analysis to demonstrate a PKC-ENH-N-type Ca²⁺ channel complex. When coexpressed with Ca²⁺ channels in Xenopus oocytes, ENH facilitated PKC modulation of current through N-type but not P/Q-type Ca²⁺ channels; expression of chimeric channels confirmed that this facilitation of Ca²⁺ current depended on the Ca²⁺ channel's ENH-binding region. Disruption of the macromolecular complex with a peptide that inhibited PKC translocation inhibited PKC facilitation of N-type Ca²⁺ current in hippocampal neurons. Thus, ENH is able to target a specific PKC isoform to a specific substrate, permitting selective modulation of Ca²⁺ current through a particular class of channels.

Y. Maeno-Hikichi, S. Chang, K. Matsumura, M. Lai, H. Lin, N. Nakagawa, S. Kuroda, J.-F. Zhang, A PKC-ENH-channel complex specifically modulates N-type Ca²⁺ channels. Nat. Neurosci. 6, 468-475 (2003). [Online Journal]